Many applications require precise sensing of the position of one object with respect to another. Prominent applications include touch screens, accelerometers, strain gauges and various other applications in metrology. Typically in these applications, the electrical capacitance between two movable electrodes is measured and used to determine the electrode spacing. Optical methods, e.g. laser interferometers, require large optics and sophisticated control functions. Other methods exist but these are typically less sensitive or achieve sensitivity only in combination with large form factors. Resistive strain gauges, for instance, require large displacements to achieve the required resolution, rendering them unsuitable as probes for highly localized measurement. Other, more sensitive sensors such as those based on the piezo-resistive effect require a significant electronics overhead. Such sensors are also relatively expensive and do not meet the requirements of all applications. For example, in touch screen applications there is a requirement for transparency, and possibly also flexibility of the screen.
With conventional sensors having the required sensitivity, the individual sensors cannot easily be integrated into existing micro-electronics components due to their large form factors. Capacitive position sensing in particular does not scale well towards larger integration densities. Use of conventional techniques is therefore problematical if extremely sensitive measurement and/or extreme miniaturization is required.
German Patent Application No. DE102004013305A1 discloses a sensor layer in which electrically conductive atomic or molecular clusters are embedded in a matrix of insulating or poorly conductive material. Conductivity of the layer due to electron tunneling between clusters varies with changing inter-cluster distances caused by strain.
“Molecular Junctions based on Aromatic coupling”, Wu et al., Nature Nanotech., 2009, Vol. 3, Pages 569-574, proposes as a plausible formation mechanism of a molecular junction the effect of π-π stacking of molecules at the ends of two gold electrodes formed by rupture of a gold wire.